Time lag fuse



Aug. 10, 1943. L. SCHMIDT ET Al. l 2,326,257

TIME LAGA FUSE Filed DSC. 4, 1941 4/ MHH...

INVENTORS Patented Aug. 10, 1943 UNITED STATES PATENT OFFICE TIME LAG FUSE Lambert Schmidt and George Schmidt, Leeds, N. Y.

Application December 4, 1941, Serial No. 421,552

13 Claims.

This invention relates to improvements in fuses of the plug and cartridge type and more particularly to improvements in fuses of the above type known generally to the art as time lag fuses.

An object of the present invention isfto provide iuses as defined above by simplified construction wherein means are provided for imparting a delay or time lag to the destruction oi the fuse element upon a predetermined overload.

Another object of the invention is to provide a luse of the foregoing character in which the fuse element is held in intimate contact with a heat absorption member, which absorption member is so selected as to retard the fuse action of the fuse strip a predetermined time interval after the initiation of a predetermined overload.

Another object of the invention is to provide a heat absorption member of insulating material and of such size and characteristics relative to a fuse strip as to delay the fuse action of the strip a predetermined time interval upon a designated overload.

A further object of the invention is to provide a fuse so constructed that the fuse element is held in contact with a heat absorption member having a different coeflicient of expansion than that of the fuse element whereby continued overload will, after an interval of time, cause expansion of the fuse element out of contact with the heat absorption member over a part of its length so that such element can rupture due to the excess heat therein.

In carrying out the foregoing and other objects of the invention, a time lag fuse embodying the same can lbe incorporated either in a fuse plug or in a cartridge type fuse. When embodied in a fuse plug, such plug is preferably made up of a base member of insulating material, a hollow top member likewise of suitable insulating material, a fuse element within the plug and a metallic shell securing the parts together. In addition to these members, use is made of a heat absorption member of suitable insulating material against which the fuse element is placed in intimate contact therewith so that this heat absorption member can act to absorb heat generated in the fuse element due to an overload of current therethrough. This heat absorption member is of predetermined size and composition relative to the fuse element or strip so that the element and the strip have widely diierent coeiiicients of expansion. Since the heat absorption member is of predetermined size relative to the amperage capacity of the fuse strip, it follows that this member can absorb heat from the strip until the strip and the member attain approximately the same temperature after which the strip will expand relative to the member and thereafter become so overheated as to rupture. In a cartridge type of fuse embodying the invention, the fuse strip is mounted on an elongated strip of heat absorption insulating material, which absorption member is substantially semi-circular in cross-section and preferably with a groove or channel in the flat top surface thereof. This channel can slope downwardly in each direction from the mid-point to permit a better intimate contact between the fuse strip and the bottom of the channel. If desired, units composed of fuse strips and heat absorption members can be made by fastening fuse strips to such mem-bers in more or less permanent condition so that elements can be replaced in a cartridge type fuse by simple insertion of a preformed unit therein.

Other features, objects and advantages of the invention will become apparent by reference to the following detailed description of the accompanying drawing wherein Fig. 1 is a vertical section through a fuse plug embodying the invention;

Fig. 2 is a perspective View of some of the elements of the fuse plug construction, such elements comprising the base, the fuse strip and the heat absorption member;

Fig. 3 is a central longitudinal section through a cartridge type fuse embodying the invention;

Fig; 4 is a section taken substantially on the line 4 4 of Fig. 3, and

Fig, 5 is a plan view of a replaceable unit embodying the invention and adapted to be introduced into a renewable cartridge type fuse.

Referring now `to the drawing and particularly to Figs. 1 and 2, IU indicates generally a fuse plug of more or less convention character and embodying the present invention. This plug is made up of a base member Il of some suitable insulating material and a top member I2 likewise of suitable insulating material, such as for example, glass. The base member I0 has a through aperture in the bottom thereof for the reception of a terminal member I 4 having a hollow neck I5 extending into the aperture.

One end of a fuse strip element I6 is secured in the neck part I5 of the terminal I4 by a metallic spring retaining member I1 in the manner set forth in the Patent of Lambert Schmidt, 2,276,703, dated March 17, 1942. This fuse strip I6 extends upwardly from the throat I5 through a notch in the bottom sidewall of a heat absorpf tion member I8, the bottom of which extendsV into the base member and .which has a flange resting on the to-p of the base il. Theiuse strip also passes under this flange. Member I8 can be secured in place by friction or any other suitable manner. The strip l@ extends across the bert. When such separation occurs, it is evi- Y dent that the separated part of the strip imme- Viiange E@ underlying the base l! and having" its sidewall rolled into threads to engage the thread formations on the periphery of the member I2. The fuse strip l5 has a narrowed Zone 2l so located as to lie substantially midway across the top of the heat absorption-member i8.. The

,top part of member ES can be shaped as shown for convenience in predetermining the mass thereof..` Y

The heat absorption member I8 is made of some.V suitable insulating material which is not aiiected by ,heat7 such as an asbestos compound, or a cold moulded compound, o1? suitable ceramic material. llfhe fuse strip lli is adapted to be held or strapped into intimate contactwith the meme ber i3 for the purpose to be explained later. The sizeand material oi'the member I3 are `determined inrelaticn to the amperage capacity of the fuse strip B to secure the proper interval of time lag upon a predetermined percentage of overload Vpassing through the strip. For a given amperage capacity fuse strip, the member I8 must be of such size and of such heat absorbing properties Vthat it can absorb heat from the strip for a predetermined length of timev lbefore the strip is ruptured atits narrow zone 2l.A Since the member i3' is made of any of the materials speciiied and since the strip 277i is made of the usual fuse metal such as some suitable zinc com-V position, it follows that these parts have chi-tier- Yent vcoeiiicients, of expansion with that of the member i8 considerably lower than that of the strip i5. t Y t The operation of this device is substantially as follows.V Upon the existence of an overload; through the strip i6, such overloadY causes the strip to become heated but the heat is absorbed from theY strip as it is generated, such absorptipn being accomplished by the member` i8.v I Ziepenwcl-Y ing von the mass of this member idand its-heat absorption; properties, thev absorption of heat from the strip will `continue for a predetermined diately acquires a high temperature due to the .overload with the result that the strip fails at its narrow zoneri in the'manner customary with fuse strips of conventional character. The

`failure at this point causes thecreation of the usual arc but such arc is of relatively short length, and lesion,v usually attendant upon rupture of a iuseV strip, is eiiminatedV due to the fact that one side of the strip rests on the heat absorption member and isrcocled ofi progressively away from the 'weak point. As before pointed out,` the mass of the heat absorption member can be determined accurately relative to the amperage capacity of the fuse strip to obtain the desired time lag in operation of the fuse for a given overload. lBy actual tests, it has been proved that the mass Yoi the neat absorption member Vis too small the iuse strip is ruptured before the proper time lag has occurred, while ii the mass ci the heat absorption member is. toO.

fioV

large,- rupture will not occur under the given overload as too much heat is. conducted away from the strip for the proper operation thereof.

YAs for example, the mass oi; the heat absorption member may be accurately determined Vso Ythat with a definite overload of the order of s ay A%, the timejlag in the operation of the fuse strip can be made to attain aperiod .of mim 1 utes or any other interval that` may be'desired. These, figures are given for illustrative purposes only. Under the same Conditions a smallerroyerf4 load will naturally extend the period of time lag while this time iag period shortens progressively as the period oiV overload increases, bearing in mind, however, that with; ashortV in the circuit including the iuseeiemeht, the operation of this fuse Velementari breaking down is substantially instantaneous, Ysince the heat generated in the strip due to the short is .so intense that thev heat absorption member cannot cool theistrip. enough to prevent the desired rapid action.

. In the @rangement shown in Figs. 3: to. 5 inclusive, .invention has. been embodied in a fuse of thecaitridge type, which. device come prises a Ygenerally tubular casing dit made of some suitable insuiatingV material such as ber .orY the like."Y Secured. to one end o theI casing` isan externally threaded member di, the. end ot which is partially` closedrby an integral at t2 having. a smallY openingy d6. adjacent one edge. of the member Ill. This. nat i2- extends across Y the endet-,the member @if to, closefmoreY than Y to. be described. later`- A second externally` lengthwofvv time or until the member litre ches a temperature close to that of the stripfl.,` 'VhenE such condition` exists, which will occurY if the overload is sufcient, continued heating o i the4 l stripfl willcause expansion thereof relative,toy

the ,member Viii' since theseY parts have diierent coeicients of expansion. TheV expansionkof the strip it` is limited to that portion thereof erg--V tendingk across the topof 'thev member ifi sincethe portions oitheistrip extendingY along the sides of member it?V are heid against expansion kby the close rit between the strip, therrnember. i3(v and the inner Wall of the top part` l2; or tlfle;

casing. Consequently, the expansion o the strip, tis confined to thiszonek across the top ot the. member [Swith the result thatthispartotthe.

stript lifts out oi yContact withthe top1 of. meme.

,detent te. to. engage the notch di.;

threaded member 55. is. secured to the otherendl of theV tubular member liisfbut such second. meub.. ber d6. is substantially openwith the exception of a notch di. at one. point along its edge. conjunction Ywith this. end .ot the assembly, use is made of apartial disc member 32 having ai, Removable; terminal cap. members. 557i; and. tit are internally.-

Vthreadedto be attached: to. the. respective. meme.

bers il and (it.

in this type of: fuse, units. embodyingthe. ine. vention` canV be utilized. andf each kof such units.y comprises .a heat absorption: member 5%- of InaterialA similar to. the. member it. The member "as shown in the drawing is. an elongatedi memberl of substantially. semi-circular. shape cross-.section with. a groove .orchannel. inthe. flat -top surface.- thereof.,.'the bottom off-Which-z www channel slopes downwardly in each direction from the mid-point. Positioned in the channel is a 'use strip element 56 having a narrow zone 51 at its mid-point. This strip 55 can be fastened to the heat Aabsorption member 55 by two clip members 58 near each end of the member 55, such clip members overlying the strip and partially passing around the outer surface of the member 55. Y

Units of this character may be made in preassembly as shown in Fig. 5 andinserted into the cartridge fuse casing as they may be desired, it being understood that this type oi' device constitutes a renewable cartridge fuse. The insertion can be accomplished in the manner customary with ruses or' this type by removing the terminals 50 and 5l, removing the partial disc M8 and introducing a unit into the housing 40 through the open end surrounded by member liu. One end or the fuse strip 5b is then passed through the opening 45 and -bent around the outer end surface oi' the partial closure 42. This end can then be clamped in place by the terminai cap 5U. The other end of the fuse strip ou" can be bent around the outer end of the partial disc i8 which has been placed in position paitiaiiy closing the end oi' the member b and this second end of the iuse strip locked in place by tneterminal cap 5i. g

'lne operation of this embodiment of the invention is similar in all respects with that expleinen hereinbefore in connection with the Pig. i embodiment of the invention since the heat absorption member can be of predetermined character to perform the functions described previously in connection with the strip be, bearing in mind the amperage capacity of the strip and tne desired time lag for a definite overload. 'he clips 53 aid in localizing expansion of the strip 5U to that portion of the strip between the clips.

From the foregoing it will be seen that the present invention provides a new type of time iag i'use in which all moving parts have been eliminated and which possesses the advantage of utmost simplicity. As before pointed out, any desired time lag with a given overload can be obtained in either of the illustrated devices by properly determining the mass of the heat absorption member relative to the amperage capacity of the fuse strip, the heat absorption characteristics of such member, and its coefficient oi' expansion relative to that of the fuse strip. All or' these characteristics can readily be determined to adapt the device for any desired operating ranges. n

It is to be understood that the invention can be modified beyond the illustrated embodiments and consequently any limitations imposed thereupon are to be only those set forth in the following claims.

What is claimed is:

l. In a time lag fuse, a casing, a member of insulating material Within said casing, and a fuse strip initially held in intimate contact with the surface of said member, said member being of heat absorption material and of such mass relative to the amperage capacity of said stn'p as to absorbfheat from said strip for a predetermined length of time upon a given overload through said strip, and said strip having a greater coefficient of thermal expansion than said member and having a zone of reduced cross section adapted to move out of contact with said member upon continued overload heating of the strip.

2. In a time lag fuse, a casing, a substantially stationary member of insulating material within said casing, a fuse strip initially held in intimate contact with the surface of said member, said member being of heat absorption material and of such mass relative to the amperage capacity of said strip as to absorb heat from said strip for a predetermined length of time upon a given overload through said strip, said strip being so held in said casing that expansion of the strip is localized, in a. portion thereof, and said strip having a greater coeiiicient of thermal expansion than said member whereby said portion oi" the strip is adapted to move out of Contact with said member upon continued overload heating of the strip. a

3. In a time lag fuse, a housing, a member of insulating material within said housing, a fuse strip initially held in intimate surface contact with said member, said member being of heat absorption material to absorb heat from said strip, said member and said strip having diri'erent coefficients of expansion whereby separation of the strip from the member occurs upon continued overload heating of the strip and member.

4. In a time lag fuse, a housing, a member of insulating material within said housing, a fuse strip initially held in intimate surface contact with said member, said member being or' heat absorption material to absorb heat from said strip, said member and said strip having diiferent coefficients of expansion whereby separation of the strip from the member occurs upon continued overload heating of the strip and member, the zone of such separation being limited to that part of the strip passing over the top of said member.

5. A time lag fuse plug comprising a casing made up of a base, a hollow upper member and a shell holding said parts together, a member of insulating material secured on said base, said member having a rounded top, a fuse strip secured in said casing and having a portion initially in intimate surface contact with said rounded top, said member being or neat absorption material of such mass as to absorb heat from said strip and prevent expansion thereof for a predetermined period upon a given overload through said strip, and said strip having a greater coeicient of thermal expansion than said member whereby a portion of the strip moves out of contact with said rounded top upon continued overload heating of the strip.

6. A time lag fuse plug comprising a casing made up of a base, a hollow upper member and a shell holding said parts together, a member of insulating material secured on said base, a fuse strip secured in said casing and passing ovei said member initially in intimate surface contact therewith, said member being of heat absorption material of such mass as to absorb heat from said strip and prevent expansion thereof for a predetermined period upon a given overload through said strip, and said strip having a greater coefficient of thermal expansion than said member whereby a portion of the strip moves out of contact with the top of said member upon continued overload heating of the strip.

7. A time lag fuse plug comprising a casing made up of a base, a hollow upper member and a shell holding said parts together, a member of insulating material secured on said base, a fuse strip secured in said casing and passing over said member initially in intimate surface contact therewith, said member being of heat absorption Y 'material of such masses to" absorb neat from said 'toman pat-rt everlyirrgrtne topef said mem i sti-ip andpreven-t expansioirtli'ereof"for a pred@ termined period upon a: given overload tir'oi-i seid stripl expansion ofsid 'strip being lir'ted tien of' the st 'ipy moves' ont of eforitafctv Witiivtlie top of seid member' upon eor-itined overleed Y iietingA of the strip;v

surface Contact with absorb heat from such strip for `et predetermined lengtiro time uponi ay giveni overload through seid strip, and" said't strip* end'A memberhavngdifferent) between a portion* ofithe" strip andlmenen-is removed upon continued overloady heating of the strip'and member: '9; A time-lag'lf-use' comprisingaJ -sustantiily tubular casing; arr elongated memlerwitli's'ai casing, and 'a fuse'strip initially-I hei.AA ir int-imt-e surace-contaetwithsaid eiongateff member, said member being) ofneat@'elsorp'tilonl mettermi tel "essereheat from suoli strip for'13,-predeterx'nined' lengtir ofVV time VuponY es giVen-overoad through seti" Vstrip; said'- Strip= arnd' seidg member Hving d rent ooeeien'ts ofexpa'nsio'n whereby con;

K teet-betweenseid-strip andf'apa'rt of said mem# ber is removed uponcontinued.1 overbadiieatirig ofthe stripendmember.

, Arepletcementiitiiit for cairtridge'typeltime 13g fusesV comprising-anelongate'dmember of insulating materiel; afuse strip positinedfon a. surface ofA said member', and means for' retainingsaid" strip*initiallyI i'rr intimatesuriaee' c'ontezet witii the member, seidm'emlder beingl made' Oil heat-aeserption" materistlf of predeterrri'ined mas'sf reiett've tothe amperagecapaeity o'isaid strip,l an seid strpand member having diierentcoen eeients of thernl exierxsibrii Whe-rey eonteet tic-:tween a portion of` the stip remeved .upon i continued?overloadlheeeting of'te stripfandlmember.-

said-elongated member, seid member being Vof heat absorption rrlirtteristlf` to Y Y instesdrfece cori-tact weer Y Sermide-mettermi of predeterriiined mass relative to' the' rlperage ciaity ofl Seid strip',` sind said strip and member having different coiicients of tiemljekparsion whereby enteet between a portion of the `stl'p and tHe-betto'm of tHe-groove is'rei'oved uponL continued overload heating oi tne'str'ip and meme-en A' 1121 replacement unit for cartridge type time I'tg fuses omprising anelongated substeintialiy selieyl call Vnieifiiber Vof insulating material, seid rrerrdoerv having a" groove' in tne fiat surface ti'iereothe ixottorri` of said grooteA sloping down: Wardyfrom tlie mid-point'i each# direction longitudinll'y of trieA memberfa fuse-strip' positioned insa-idgrove; and; means' for retaining sfi-dstr-ip initially in' intimato surface conta-et- Witiithelote Ytorri of said groove; said rneiiser'v being made of sorptierrmateriel'of predetermined mass relative to-Yte'- amperg'e cpacity o'-saidf strip to absorb ifeett'froml and delay eXpansior--ofthe-strip' for al# predetermined# period for a---g-iveir overload tiirr'aug'hst-iestliip, seidA stili-p1 havingL af greater ceeo'entfoi therme-11 expansion' than sat-idJ meme insulating malt-evier, 

